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1. Foreword In the process of power plant information construction, more and more experts, scholars, and power engineering designers are aware of the importance and urgency of promoting field bus technology in power plants. Many papers have been proposed based on fieldbus technology. Control system application ideas and recommendations in the power plant. But so far, in the case of domestically-built and under-constructed power plants, the real-world example of comprehensive and systematic application of fieldbus control systems has not yet been reported. It is only local pilot applications that are available in the literature. Everyone holds a positive and positive attitude to fieldbus technology on behalf of future power plant automation, but why is it difficult to enter into substantive applications in engineering design?
In order to facilitate the following discussion of this issue, although the meanings of the fieldbus and fieldbus control systems have been repeatedly described in the relevant literature, I still think it is necessary to first quote the International Electrotechnical Commission IEC and experts on what is the fieldbus And the definition made by the fieldbus control system.
According to the definition of the International Electrotechnical Commission IEC 61158 standard, a digital, serial, bi-directional, multi-point communication data bus installed between a field device in a manufacturing or production process area and an automatic control device in a control room is called a field bus. The control system consisting of fieldbus and field intelligent devices is called Fieldbus Control System (FCS). The measurement of whether a control system is a real fieldbus control system FCS has three key points, namely: core, foundation and essence. The core of FCS is the bus protocol. Only the control system that conforms to the fieldbus protocol can be called the fieldbus control system. The foundation of FCS is the digital intelligent field instrument, which is the hardware support of FCS; the essence of FCS is the on-site information processing. It is the performance of FCS system.
From the above definition, it can be seen that the fieldbus control system is a new type of computer-based, all-digital, two-way communication control system. The essential difference between it and DCS lies in the digitization and networking of field-level equipment, which enables two-way communication between the control device and the field device and eliminates the "blind spot" of information for production process monitoring. It can be said that field equipment-level digitalization and networking are the basis of power plant information management.
2. The characteristics and status of fieldbus technology The development of CPU technology has led to the digital revolution of field instruments and devices. It has also made digital communication between field instruments and devices possible. Digital, intelligent field instruments and devices (such as sensors, actuators, etc.) not only replace the 4-20mA analog system, but more importantly, they can realize control functions and device management functions in field devices, and have digital communication. , in the control room can get a lot of information on the field equipment, such as diagnosis, measuring range, configuration and identification. With the advent of field bus technology, many field device signals originally requiring a large number of cables for point-to-point connection can be transmitted through a single network cable, which can significantly reduce the cable usage and reduce the related materials and installation costs.
The starting point of fieldbus technology development is to provide users with open, interoperable, interchangeable, and uniform standards of measurement and control products, overcoming the control of traditional DCS and PLC control systems with patented technologies. Closed issues, the preferred selection of different company's products, integration of the best production process control system, reduce construction project and operating costs, improve the competitiveness of enterprises.
Based on the discussion of relevant data, compared with traditional DCS and PLC control systems, the superiority of FCS based on fieldbus technology is summed up in the following aspects:
(1) Interoperability (2) Dispersibility (3) Reliability (4) Accuracy (5) Openness (6) Economicality (7) Maintainability.
These features and advantages are described in detail in related literature and will not be repeated here. Since there are so many benefits, why are we not actively using it? This leads to the standard battle of the field bus and the limitations of the field bus itself.
First of all, as a result of the fieldbus standard dispute, IECTC65 (the 65th standardization committee responsible for industrial measurement and control) passed eight types of fieldbuses as the IEC61158 international standard at the end of 1999. In August 2001, 10 types of fieldbus standards (Third Edition) were revised and formulated:
Type1TS61158 Fieldbus Type2 ControlNet and Ethernet/IP Fieldbus Type3 Profibus Fieldbus Type4P-Net Fieldbus Type5FFHSE Fieldbus Type6 SwiftNet Fieldbus Type7WorldFIP Fieldbus Type8 Interbus Fieldbus Type9FFH1 Fieldbus Type10 PROFInet Fieldbus (April 2003 became an official international standard)
In addition to the above 10 standards, there are the fieldbus standards SDS (SmartDistributedSystem), Asi (ActuatorSensorInterface), and DeviceNet passed by IECTC17B, and the CAN protocol of ISO11898, as well as some European standards. Such a large number of standards have brought great confusion to the user application, which has led to the fact that there is no de facto uniform standard, because different fieldbus standard protocols cannot directly interconnect and communicate with each other.
Secondly, the above-mentioned various field buses are developed for different application fields, and the field buses themselves have limitations in their application fields.
In the field of factory automation, discrete logic control plays a dominant role because factory automation contains fast moving machinery and has a faster response than slower process automation. Fieldbus types suitable for such applications are DeviceNet, ControlNet, Profibus (DP and FMS Application Profiles), and Interbus, ASI (AS-Interface).
In the field of process automation, continuous regulatory control dominates, but it also includes discrete or digital control. Fieldbus types that are suitable for such applications are FoundationFieldbus, Profibus-PA, WorldFIP, and others.
3. Control characteristics of the power plant's production process The power plant's production consists of the following major processes: fuel system (transportation and storage of coal and fuel/gas), thermal system, and boiler and steam turbine generator sets (convert the chemical energy of fuel into Heat energy and thermal energy convert water into steam, steam heat energy is converted into mechanical energy in a steam turbine, and then converted into electrical energy), a slag removal ash system (solid waste treatment of a combustion product), a desulfurization system (atmospheric discharge treatment), and water Treatment system (including clean water, boiler make-up water, wastewater, condensate polishing, chemical sampling and dosing, etc.), power distribution system (including plant power system, booster station, etc.). It can be seen that electricity production is an extremely complex industrial process that covers the contents of factory automation and process automation. In the traditional power plant control system mode, DCS is usually used as the main control system in the heat production process of the main power plant area, and other auxiliary systems use the PLC as the core control system. Because the field-level equipment mainly uses the traditional analog and digital signals, the monitoring of the production process can only reach the I/O subsystem.
In the process of electric power construction in recent years, the information management of electric power production enterprises has attracted extensive attention and invested a large amount of funds to build auxiliary control system networks, power plant real-time monitoring systems (SIS) and power plant information management systems (MIS). For the field-level devices, traditional devices and methods are used to access the control system I/O subsystem. This is undoubtedly the "passive water" for information construction with the expected goal of predictive equipment maintenance and equipment management. Therefore, the fundamental way to solve the “information blind spot†in power plants is to use smart field devices that support field buses.
4. Problems with the application of fieldbus technology Although the fieldbus technology has a series of features and attractive advantages, despite the growing demand for the construction of digital and informatized power plants, the power design institutes and construction units try to use the site. Bus engineering is one of the few. The main obstacles to application have been analyzed in some literature, such as:
(1) There are many fieldbus standards and users have no choice.
(2) There are fewer specifications and varieties of intelligent field devices that support the fieldbus standard, and fewer domestically-made devices support the bus standard, especially for smart devices developed by the power plant, which cannot meet the needs of the various specialties of the power plant.
(3) The price of smart field devices supporting fieldbus standards is high. Although the cost of hardware and software of the control system based on fieldbus technology is equal to or slightly higher than that of DCS, the entire project life cycle cost of FCS for control system design, construction, commissioning, operation, and maintenance is indeed much lower than that of DCS. . This kind of benefit is often the problem that investors and construction units may not pay enough attention to at the project planning stage.
(4) The network connecting the bottom layer of fieldbus devices does not support redundant structures.
In addition to these application barriers, I believe that the following constraints have limited the application of fieldbus technology in power plants.
(1) Infrastructure model of existing power plants. At present, most of the purchases of power plant control equipment are prepared by the Design Institute. The construction unit organizes purchases. There are also some equipment purchased by the construction unit, and other control equipment is supplied by the main equipment factory or subcontracted. It is difficult to guarantee the procurement of such equipment according to a unified bus standard. According to the actual situation at present, even if the technical conditions in the specification book are very clear, the arrival of goods on the spot is another matter. Different field bus standards are incompatible, resulting in no money.
(2) Within the design institute, automatic control involves electrics, thermal control, and even system majors. These professional management systems and field devices are different. For example, in the main building, the switching stations of the pumps and fans (SWITCHGEAR) and the PC and MCC equipment are under electrical control, and the electric door MCC is under heat control. Hundreds of devices require a unified fieldbus standard for electrical and thermal control when designing and ordering, which is difficult to imagine.
(3) The technical personnel of investors, construction units, construction units or even design institutes lack of in-depth understanding of field bus technology. Fieldbus is a new type of control system. As a technician of the fieldbus application, especially if the thermal design engineers of the design institute are still unable to design a reasonable fieldbus control system for DCS, they will not be able to use the fieldbus. The advantages of the bus do not even guarantee the normal operation of the fieldbus control system. For example, fieldbus FF and Profibus-PA support bus power supply, but there are restrictions on the number of field devices connected and the communication distance of the bus, and appropriate terminal devices must be set up. Therefore, it is necessary to be familiar with the characteristics of field buses and smart devices. In order to ensure the correctness of the bus design. For another example, only the FF bus protocol supports programming languages ​​for establishing control strategies. That is, only smart devices that support the FF bus protocol, such as the valve positioner, can be used as regulators and perform PID functions on their own circuits. Control functions are distributed to the site. Equipment, system functions and faults are more dispersed, which further reduces the load on the central controller, improves the system performance, and reduces the number of central controllers. However, Profibus technology does not have a programming language for control strategy. That is, field devices that support Profibus-PA cannot implement control strategies. Control must be performed by the central controller. However, the Profibus-supported product range is more complete and extensive than the FF.
These characteristics must all be considered by the designer when choosing a fieldbus standard.
(4) Restrictions on design concepts. We have always emphasized that the control system applied in the power plant must have been successfully applied in 2 units of the same type for more than 3 years. It should be noted that fieldbus technology has been developed for more than a decade. Intelligent devices supporting fieldbus technology have been basically matured and have been widely used in petrochemical and other industries. The nuclear power plant user requirements document prepared by the American Electric Power Research Institute has used the fieldbus as an option for the nuclear power plant control system in the UDR document. This should provide inspiration to the application of field bus technology in the thermal power plant.
(5) The lack of a reasonable design cycle. Now the engineering design cycle of most power plants is greatly compressed, so it is very tight from the design institute to complete the design according to the conventional scheme.
(6) The lack of innovative mechanisms and motivation for designers. The application of new technologies in the project will always have certain risks. This requires designers to invest a lot of energy in research and program demonstration. However, the reality is often no additional investment in the application of new technologies, especially the successful application of new technologies. There is no special reward mechanism.
5. Power Plant Application Fieldbus Technology Objectives and Countermeasures Although the market and engineering practices have not been used in the real sense of the fieldbus control system power supply plant, it does not mean that we do nothing in the fieldbus technology. As long as we recognize the true purpose of using fieldbus technology and overcome the obstacles that restrict the application of fieldbus technology in power plants, we can make fieldbus technology play a positive role in power plant automation and informationization.
First of all, we must avoid misunderstanding of the fieldbus for the fieldbus during the planning and design of the power plant automation and informatization program. The information platform and enterprise management system for reducing the life cycle cost of power plants and building companies with reasonable investment should be regarded as the common goal pursued by investors, construction units, and design institutes. Based on such principles and guiding ideology, we will realistically study the automation and information products that control technology, computer technology and communication technology have brought to us, and build power plant monitoring and information management systems.
In the planning process of power plant automation and informatization, it is still necessary to combine the characteristics of each process and production process of the power plant with the most suitable fieldbus standards and detection and control devices. It should not be mandatory to uniformly apply a fieldbus standard throughout the entire plant. It is neither possible nor necessary that the entire plant is to be a fieldbus standard. In the monitoring layer and information management layer, industrial IT technologies such as Ethernet and OPC protocols, switches, and gateways have provided interconnection technologies between different networks.
It should not be over-emphasized that FCS, DCS or PLC+ fieldbus are used in the project. As long as the above principles are met, it is the most suitable control system. The debate over the replacement of DCS and PLC systems with FCS is also insignificant.
After an in-depth understanding of the existing fieldbus control system, we will find that, in addition to the FF bus field smart device can achieve part of the field control strategy, the logic control also depends on the main station or the central controller, other bus systems are also using the central controller . Although these central controllers can be miniaturized and site-arranged, they still require centralized computing and processing (in some cases the central controller can save I/O processing and the controller also needs redundant settings). From the analysis of the overall structure of fieldbus control system, it is still similar to the hierarchical structure of DCS, but the network protocol is more open. The system integration mode will not change significantly at present. We do not seem to be able to completely separate from the products of mainstream DCS manufacturers in the near future. It is entirely by the design institutes or engineering companies to use the products of mainstream or non-mainstream DCS manufacturers to integrate the control of the power plant. system. Of course, in this process, the author does not deny that after the design institute has made major changes in design patterns and design depth, it closely cooperates with mainstream DCS or other types of control system suppliers and, like the design institutes of the petrochemical industry, assumes a greater scope. The content of the work and the depth of the design of the DCS or fieldbus control system. Just as the early control system used component metering, the design institute took on the configuration and integration of the entire power plant control system. However, with the application of DCS and PLC, the design institute's ability in this area has been depleted.
Here are a few ideas to discuss with you:
(1) Investors and constructors play a key role in using fieldbus technology. Without their support, the role of design institutes is limited. Because it involves project investment and technology risks. Design institute automation designers should take the lead and promote the application of field bus technology. However, the design institute should make a thorough technical analysis report on the application of fieldbus technology, clarify the advantages and disadvantages of the application of fieldbus and investment estimates, and put forward a practical project implementation plan and risk response plan.
(2) The design institute should have a sense of innovation in the application of fieldbus technology. The management should create a design innovation condition and environment for the designers. To solve the current situation in the control system planning of thermal and electrical two majors, we must pay full attention to the overall planning of the whole plant automation and informationization program, and if necessary, properly integrate the division of labor of the two specialties. In the application of fieldbus technology, some power design institutes have made useful attempts and accumulated valuable design and application experience, such as Shandong Laicheng Power Plant, Jiangyin Xiagang Power Plant, Yunnan Xuanwei Power Plant, Guizhou Nayong Power Plant, Zhejiang Ninghai Power Plant, Shandong Weihai Power Plant, etc. At the preparation stage of the bidding document for the control system, it is necessary to extensively understand the capabilities and solutions of mainstream and non-mainstream DCS products that support fieldbus, and organize relevant experts to conduct the necessary argumentation. Regardless of host bidding, tendering for auxiliary equipment or bidding for auxiliary systems, and bidding for DCS and PLC systems, product requirements that support the application of on-site standards must be defined as a necessary condition.
(3) Investors and construction units must provide enough design cycles for design institutes to adopt field bus technology design schemes, and provide necessary support in terms of technical program demonstration and product design selection. After determining that the project uses a certain type of bus standard, the design institute should have more autonomy in the field of bus products. Because the selection of bus products requires more detailed design and cooperation of suppliers, including detailed specifications and specifications, as well as parameters and options, rather than allowing the design institute to list the process parameters of the detection and control devices, without specifying the specific requirements. Model and supplier practices. The construction unit can change the previous practice of the control device supported by the system integrator. The PLC used by each auxiliary system can determine the appropriate two bus standards for centralized bidding and procurement, so as to facilitate the unification of field device bus standards.
(4) Because the field bus is different from the conventional design, the depth and difficulty of the automation major of the design institute have been improved, so the corresponding design cost and design quota must also be adjusted reasonably.
(5) Automated designers must strive to improve their own business level, change current practice in the design of conventional DCS and PLC systems, and master and apply field bus technologies and products. This requires leadership from all levels of the design institute, especially the departments. Pay attention to and strengthen the technical training for designers. Currently, the Design Institute is almost not involved in the network construction and configuration work of the DCS or PLC system construction drawing stage. It is only responsible for providing P&ID, preliminary I/O inventory, and finally completing the external wiring diagram of DCS or PLC. The depth of each design institute may differ from this, but generally it does not go deep into the internals of DCS and PLC systems. The consequence of this is that the design institute does not have a thorough understanding of the control strategy of the whole plant, and the system configuration method and function distribution are not well understood. Therefore, design institutes have less and less power to talk about system optimization, network configuration and function allocation. The author believes that to reverse this situation, design institutes should seize the opportunity of applying field bus technology and deepen the design depth. This depth is mainly reflected in the following contents: P&ID diagrams, instrument position layout diagrams, adjustment block diagrams and logic diagrams, device specifications and data sheets, wiring diagrams, power supply configuration diagrams, and so on.
When using the FF fieldbus, the P&ID diagram work becomes particularly important. The depth of the existing P&ID diagram is to be improved because in the case of the FF fieldbus standard, the control strategy of the system and the equipment needs to be planned through P&ID. In the design of P&ID diagrams, the concept of regional design needs to be introduced. In order to achieve reliable and complete regulation function and logic, usually all I/Os of a loop should be in the same area, and each area can have 2~6 loops. The use of P&ID should ensure that all points related to the area loop are within that area. Not only that, but also learning and mastering the fieldbus wiring, wiring technology and calculation methods. Because the fieldbus wiring is different from the conventional DCS and PLC control system wiring. The field bus area design will replace the traditional I/O distribution wiring. In order to accurately estimate the length of the fieldbus network cable, to plan a reasonable network connection, to avoid the on-site signal to and from the system, affect the system response speed and control performance, you need to rely on the layout of the field instrumentation and control devices. The role of the instrument location map is to determine the location of the network backbone and branch and junction box, this can ensure that the bus installation meets the requirements of the area length, branch length and terminal location, and the successful installation and work of the field bus. In addition, there are three kinds of topological structure of the field bus network: The bus has the branch structure, tree or branch or chicken claw structure, daisy chain topology. Different structures are suitable for different occasions, to avoid the use of daisy chain topology, it seems to reduce the cable and installation costs, but the system maintenance and reliability is extremely unfavorable. As a designer, you must understand and master this. The power configuration has similar problems and will not be repeated.
It must also be realized that many existing fieldbus devices have been connected using connectors. If the design institute still holds the thinking mode and working attitude of only the DCS cabinet external terminal block diagram, the control strategy and logic diagram The work and push the prefabricated cables and connections to the integrator's scope of work, then when the control system developed to the connection between most of the system equipment using prefabricated cable and connector mode, the Design Institute automation professional survival means? But if we take a quick step today and change the thinking of today's design, the Design Institute will also face new opportunities. The author thinks that in the design of the fieldbus control system, the use of 3D network cabling design technology in the future is an advantage of the design institute, and it is also a role that the general control system integrator can hardly replace.
(6) We are concerned about the redundancy of fieldbus. For example, FFH1 and Profibus-PA do not support redundant networks and should not restrict the application of fieldbus technology. After we have thoroughly analyzed the characteristics of the power plant's process flow, we should boldly adopt field bus technology in our design. In the process of two-way hot-standby or multi-channel configuration of equipment and systems, even if the bus short-term interruption will not affect the system's safe operation, because the system itself has adopted redundant settings, and like coal, chemical water treatment Such systems, generally have intermediate buffers, such as storage tanks or coal hoppers. Therefore, as long as the fieldbus network is planned rationally, just as the principle of not being able to concentrate spare or redundant points on the same card in the case of DCSI/O allocation, the field devices hooked up on the fieldbus network must also be avoided. same question. The first problems occurred when the 3UF5SIMOCOD-DP was used in the Laicheng Power Plant belonged to this category. According to the data, the original design linked the intelligent controllers of the A/B lubricant pump motors of several coal mills and fans to the same root. On the bus, daisy chain connection is used. Designs like this, even with redundant networks, cannot solve the problem of equipment overhaul and reliability. This illustrates more strongly the importance of network design planning for design institutes using fieldbus, and the necessity for designers to become familiar with the process system and operating methods.
(7) Selection of power plant field bus.
As already mentioned, it is impossible to use a bus to solve all industrial control and process control. Power plant auxiliary systems such as coal, ash, and water systems are intrinsically in the industrial automation category. In these fields, such as the petrochemical industry and the manufacturing industry, the control systems using fieldbus technology have mature experiences. And PLC still plays a major role in these occasions, so choosing the products that support the bus standards such as Profibus-DP, ControlNet are all suitable options. I believe that the application of field bus technology in coal ash discharge system can best reflect its advantages.
In the control of the thermal system of the main building, FF is the best option, and the single-loop control is dispersed to the site, just like the early-stage regulator loops, but the performance is no longer the same. However, compared with Profibus, FF's inadequacy lies in incomplete product series, which makes it difficult to build a complete and unified bus network. According to the latest fieldbus technology data, there are currently a number of suppliers of smart devices and control systems that have developed products that support a variety of fieldbus standards, which facilitates the selection of field-level bus devices. In addition, communication modules that support multiple bus standards in the field have also been introduced. In this way, field-level devices of different standards can be integrated into a DCS or PLC control system through a communication interface module. Of course, Profibus and WorldFIP in the main building are also good options. Niederhoschen Power Plant in Germany is one of the most extensive examples of field devices using Profibus. Siemens used it as a demonstration power station to promote field bus control systems. Many domestic construction companies and design institutes use this power plant as an application after returning home. Fieldbus technology reference; the second phase of Huanengqi Power Plant uses the WorldFIP bus protocol in addition to conventional instrumentation and devices.
It should be noted that in the fieldbus control system, the application of remote I/O that supports the fieldbus protocol is still a very realistic and attractive design solution. However, in the design of traditional DCS, remote I/O is still far from playing its due role. It cannot but be said that it is a pity.
(8) Immature views on the control of power plant SIS investment. Engineering construction is different from scientific research. The most essential difference is that engineering should focus on investment efficiency ratio. The author thinks that the current investment in SIS in China is too large, and its benefits have not been played out as expected. It is understood that some functional modules such as advanced optimization control, equipment maintenance, and life management that are envisaged by SIS have basically no acceptance rules and no assessment standards, and can be said to remain in the exploratory stage. Some project optimization control functions have not been included in the scope of SIS, or use a separate PC access control system via TCP/IP. In the configuration and planning of the SIS system, almost all the settings required for real-time control are kept from switches, servers, networks, and interface machines. Some common software and equipment and MIS still have duplicate configurations. It is important to note that the cycle of upgrading IT products is getting shorter and shorter. If today's network system that builds large amounts of capital is used, if the envisaged software function does not work quickly, hardware equipment may become obsolete or have a deteriorating performance in a few years, which will result in Great waste. In the past, the author has pointed out that the field device level is not digitized and networked. The predictive maintenance and status maintenance and equipment management functions of the devices and systems envisaged by the SIS are “passive waterâ€. After the fieldbus is used, some device management functions can be fully implemented within the control system itself. Of course, management information can also be passed to the management information layer. Therefore, under the condition that the SIS does not participate in the real-time and optimized advanced control mode and the two-way communication with the chiller control system is not implemented, the redundancy configuration adopted by the SIS system center switch, the network, and the server can be simplified and even fully considered. After setting up the network security system and the MIS network, it is only necessary to set up a real-time database in the MIS to achieve management's purpose of collecting, processing, and monitoring process data. The investment saved from the SIS part can be invested in the acquisition of on-site smart equipment and network construction.
6. Conclusion Rational planning of the automation and information architecture of the power plant, reduction of project cost, improvement of power plant automation and information management, and the opportunity and challenge brought by the new technology brought by the practical and positive scientific attitude should be a good requirement for power plant automation designers. Professional quality and technical quality. Fieldbus technology has basically matured. We must seize the current opportunities for excellent electric power construction, conscientiously study and strive to grasp the fieldbus technology, and actively and steadily solve problems in engineering applications. Investors, construction parties, and design institutes must change their concepts. Work with equipment suppliers to promote the application of field bus technology in power plants and enjoy the benefits and results of the new technology revolution.
Application of Fieldbus Technology in Power Plant
Abstract: This article gives an overview of the characteristics and status of fieldbus technology, describes the control characteristics of the power plant production process, analyzes in detail the many problems in the field bus application process, and clarifies the purpose of applying fieldbus technology in power plants, and puts forward in the power plant Application of field bus technology solutions and ideas.